Dual mask capacitor for integrated circuits

ABSTRACT

An embodiment of the invention is a capacitor comprising a bottom electrode  70  coupled to a first interconnect  30   a  of the top metal level  10 , a capacitor dielectric  90 , sidewalls  105 , and a top electrode  110  coupled to a second interconnect  30   b  of the top metal level  10 . Another embodiment of the invention is a method of manufacturing a capacitor using a first mask  140  to form a material stack that includes a bottom electrodes  70  coupled to a first interconnect  30   a  of the top metal level  10 , a capacitor dielectric  90 , and a partial top electrode  100 . The method further includes using a second mask  150  to form a complete top electrode coupled to a second interconnect  30   b  of the top metal level  10.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to patent application Ser. No. 10/670,037; (filed, simultaneously with this patent application) entitled “High Capacitive Density Stacked Decoupling Capacitor Structured”; patent application Ser. No. 10/335,333 (filed Dec. 31, 2002) entitled “MIM Capacitors and Methods for Fabricating Same”; patent application Ser. No. 10/638,596 (filed Aug. 11, 2003) entitled “MIM Capacitors and Methods for Fabricating Same”. With their mention in this section, these patent applications are not admitted to be prior art with respect to the present invention.

BACKGROUND OF THE INVENTION

This invention relates to a capacitor that can be integrated into the top metal level interconnect layer of an integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A—1B are a cross-sectional views of a dual mask capacitor in accordance with the present invention.

FIG. 2A—2I are cross-sectional views of the dual mask capacitor of FIG. 1A at various stages of fabrication.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described with reference to the attached figures. The figures are not drawn to scale and they are provided merely to illustrate the instant invention. Several aspects of the invention are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the invention.

Referring to the drawings, FIG. 1A is a cross-sectional view of a dual mask capacitor in a partially fabricated semiconductor wafer in accordance with the present invention. More specifically, FIG. 1A shows a dual mask high density capacitor that is formed above the top metal level interconnect layer 10 of a semiconductor wafer 20. The capacitor shown in FIG. 1A may more generally be considered a top metal level capacitor.

In the example application shown in FIG. 1A, the top metal level 10 is a single damascene metal interconnect layer. However, it is within the scope of the invention to form the dual mask capacitor over other interconnect structures such as a dual damascene metal interconnect layer.

The single damascene metal interconnect layer 10 shown in FIG. 1A contains metal interconnects 30 a, 30 b that properly route electrical signals or power throughout the integrated circuit. In the example application, the metal interconnects 30 a, 30 b are comprised of Cu. The single damascene metal interconnect layer 10 also contains regions of dielectric material 40 that electrically insulate the metal interconnects 30 a, 30 b. The dielectric material is preferably comprised of any low-k material, such as Organo-Silicate Glass (“OSG”) or Fluorinated Silicon Glass (“FSG”). In addition, the single damascene metal interconnect layer 10 may contain a dielectric barrier layer 50. If present, the barrier layer 50 functions as an etch stop layer and may be comprised of a material such as SiC.

The single damascene metal interconnect layer 10 is the top metal level formed over a semiconductor body 60. Semiconductor body 60 usually contains other metal interconnect levels that are located below—and are probably electrically interconnected to—the top metal level 10. Together, the metal interconnect levels properly route power and electrical signals throughout the integrated circuit. The semiconductor body 60 also contains a device level that is located below the metal interconnect levels. The device level may contain passive elements and active elements such as transistors. Moreover, the device level may contain various well and substrate technologies.

Only the top metal level 10 is shown in FIG. 1A for simplicity. In the best mode application the metal interconnects 30 a and 30 b are power and ground lines. As a result, the interconnect routing in the top metal level 10 is not as dense as the interconnect routing in the lower metal interconnect levels. Therefore, more space is available for the decoupling capacitors that are connected to the top metal level. In the best mode application the dual mask capacitor is a decoupling capacitor; however, it is within the scope of the invention to form dual mask capacitors that perform other functions such as a RF capacitor (i.e. analog capacitors). The use of the dual mask capacitor over the top metal level in RF applications results in a reduced parasitic capacitance compared to other locations.

The dual mask capacitor is configured in an over-metal application. More specifically, the dual mask capacitor is completely connected to the integrated circuit through its underlying metal interconnect layer. Therefore, the dual mask capacitor configuration is not dependent on the use of a subsequent metal cap layer (or metal interconnect layer) and is thereby compatible with any packaging technology.

Referring again to FIG. 1A, the dual mask capacitor includes a bottom electrode comprised of layers 70 and 80, a capacitor dielectric 90, and a top electrode comprised of layers 100 and 110. In the best mode application, the first layer 70 of the bottom electrode is comprised of TaN. This material is used in the best mode application because it is compatible with copper processes and it acts as an effective barrier to the out-diffusion of copper from the metal lines 30 a into the capacitor dielectric. The next layer 80 of the bottom electrode is comprised of TiN. This material is used in the best mode application to take advantage of the higher capacitance density obtained with a TiN/TaO_(x) interface as opposed to a TaN/TaO_(x) interface, since the TiN is less susceptible to oxidation during the deposition of the TaO_(x).

The capacitor dielectric 90 is comprised of TaO_(x) in the best mode application. However, other high-k dielectrics such as HfO_(x) may be used.

In the best mode application the top electrode includes a first layer of TiN 100 and a second, strap layer of TaN 110. Depending on the process technique used to create the capacitor dielectric 90, the top electrode may also contain impurities (i.e., carbon, hydrogen, and nitrogen). The top electrode strap layer 110 is TaN in the best mode application because it is compatible with copper processes and it acts as an effective barrier to the out diffusion of copper from the metal lines 30 b into the capacitor dielectric. The top electrode first layer 100 is comprised of TiN in the best mode application to take advantage of the higher capacitance density obtained with a TiN/TaO_(x) interface as opposed to a TaN/TaO_(x) interface. However, the use of the TiN first layer 100 is optional, as shown in FIG. 1B and described more fully below.

The dual mask capacitor is located over the top metal level 10 such that the bottom electrode 70 of the dual mask capacitor is electrically coupled to a first interconnect 30 a of the top metal level 10. In addition, the top electrode 110 of the dual mask capacitor is electrically coupled to a second interconnect 30 b of the top metal level 10. In the best mode application, the dual mask capacitor functions as a decoupling capacitor and the first interconnect 30 a is the power rail while the second interconnect 30 b is ground.

Sidewalls 105 are located on the sides of the dual mask capacitor and provide electrical isolation between the bottom electrode 70, 80 and the top electrode 100, 110. Therefore, the sidewalls 105 protect against electrical shorting between the top and bottom electrodes of the dual mask capacitor. In addition the sidewalls 105 control the substrate parasitic capacitance in circuit designs where the dual mask capacitor functions as an analog capacitor.

A protective overcoat 120 is formed on top of the semiconductor wafer 20. The protective overcoat 120 is generally comprised of an etch stop portion and an overcoat portion. Both portions are preferably comprised of SiO₂; however, any suitable dielectric material may be used.

Referring again to the drawings, FIGS. 2A-2I are cross-sectional views of the dual mask capacitor shown in FIG. 1A at various stages of fabrication. First, a semiconductor body 60 is fabricated up to the completion of the top metal interconnect level 10, as shown in FIG. 2A. The process steps used to fabricate the semiconductor wafer 200 until this stage are those standard in the industry. The last step in the manufacture of the top metal level 10 is generally copper chemical-mechanical polish (“Cu CMP”). Cu CMP is performed to planarize the surface of the semiconductor wafer 20 and to remove the excess copper and dielectric materials, and also fashion the inlaid metal lines 30 a, 30 b.

Referring to FIG. 2B, a layer 70 of TaN is now formed over the semiconductor wafer 20. The layer of TaN may be formed using any suitable manufacturing process such as physical vapor deposition (“PVD”). Next a layer 80 of TiN is formed over the semiconductor wafer 20. The layer of TiN may also be formed using any suitable manufacturing process such as physical vapor deposition (“PVD”).

Next, a layer of TaO_(x) is formed over the layer of TiN 80 using any suitable manufacturing process such as chemical vapor deposition (“CVD”). The TiN layer 80 reduces oxidation of the bottom electrode layer 70 and therefore reduces the leakage of the dual mask capacitor. The layer of TaO_(x) is annealed in activated oxygen radicals to increase the oxygen content (i.e. the value of x is typically increased to values between 2 and 3) and decrease the impurities of the capacitor dielectric 90.

In the best mode application, a second layer 100 of TiN is deposited over the semiconductor wafer 20 using any suitable manufacturing process such as PVD. If used, this second layer 100 of TiN will eventually form part of the top electrode; however, the formation of this second layer 100 of TiN is optional.

Referring to FIG. 2C, a layer 130 of photoresist is applied over the semiconductor wafer 20. Then the photoresist layer 130 is patterned with a lithography process using a first mask 140. This first mask 140 defines the outline of the capacitor stack. The capacitor stack is situated over a first interconnect 30 a of the top metal level 10; thereby creating an electrical connection between the bottom electrode layer 70 of the capacitor stack and the first interconnect 30 a of the top metal level 10.

Next, as shown in FIG. 2D, the capacitor stack is etched using the patterned photoresist 130. Any well-known plasma etch process, such as fluorocarbon-based plasma etch with an Ar additive, may be used to create the capacitor stack.

The photoresist pattern is removed with an ash process and now a layer 105 of dielectric is formed over the semiconductor wafer, as shown in FIG. 2E. In the best mode application, the dielectric material is SiO₂; however, other materials such as SiN or tetraethylorthosilicate (“TEOS”) may be used. The dielectric layer 105 may be applied through any well known manufacturing process such as CVD or plasma-enhanced chemical vapor deposition (“PECVD”).

A standard blanket etch process is used to etch the dielectric layer 105 to create the capacitor sidewall structure shown in FIG. 2F. Due to the variability in the etch rate of the blanket etch process, the height of sidewalls 105 may vary from that shown in FIG. 2F. For example, the top of the sidewalls may be located below the top of the top electrode material 100. In fact, the sidewalls can be any height above the interface between the capacitor dielectric 90 and the top electrode layer 100 and still provide effective electrical isolation between the top and bottom electrodes of the capacitor.

Next, a second layer 110 of TaN is formed over the semiconductor wafer, as shown in FIG. 2G. Once it's etched, this second layer of TaN will complete the top electrode structure. However, if the optional top electrode layer 100 was not formed (as noted above) then layer 110 will be the sole top electrode layer. The layer 110 of TaN may be formed using any standard manufacturing process such as PVD.

As shown in FIG. 2H another layer of photoresist 130 is formed over the layer of TaN 110 and a second mask 150 is used to pattern and etch the photoresist 130. This second mask 150 defines the structure of the layer of TaN 110.

The photoresist 130 is patterned with the second mask 150 also using a lithography process. The patterned photoresist 130 is then used to etch the second layer of TaN 110, as shown in FIG. 21. Any suitable etch process, such as fluorocarbon-based plasma etch with an Ar additive, may be used to etch the second layer of TaN 110. Together, layers 100 and 110 comprise the top electrode of the dual mask capacitor.

In the best mode application shown in FIG. 21, the layer 110 of the top electrode extends beyond a second interconnect 30 b of the top metal level 10. This structure ensures a robust electrical connection between the top electrode 110 and the second interconnect 30 b. However, it is within the scope of this invention to use different structures for the top electrode layer 110. For example, the top electrode layer 110 may extend partially over the second interconnect 30 b instead of past the second interconnect 30 b as shown in FIG. 21.

Next, the photoresist pattern 130 is removed using any known ashing process and the fabrication of the semiconductor wafer 20 continues with known manufacturing processes. In the best mode application a protective overcoat is formed immediately over the semiconductor wafer 20, as shown in FIG. 1A. The protective overcoat 120 preferably includes an etch stop layer comprised of SiC followed by an overcoat layer comprised of SiO₂. After creating the protective overcoat layer 120 and a bond-pad opening pattern-and-etch, any cap layer such as an electro-less Ni cap may be formed before finally packaging the integrated circuit.

Various modifications to the invention as described above are within the scope of the claimed invention. As an example, instead of using TaN and TiN for the dual layer bottom electrode, other suitable materials such as Ir or Ru, or material combinations may be used. The top electrode may also be comprised of any suitable material or material stack. For example, the top electrode may be comprised of a layer of TiAION, Ru, Ir, or TiN, followed by the layer of TaN. Furthermore, instead of a dual layer bottom electrode or a dual layer top electrode, a single layer bottom or top electrode may be used. If a single layer bottom electrode or top electrode is used, it may be comprised of any suitable material such as TaN. The metal interconnects 30 a, 30 b in the best mode application are comprised of copper; however, other materials such as Al may be used. Moreover, cleaning steps were omitted from the above fabrication explanation; however, the semiconductor wafer should be cleaned as necessary during its manufacture.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents. 

1. An integrated circuit including a top metal level capacitor comprising: a plurality of levels of metal conductors disposed near a surface of a semiconductor substrate, the plurality of levels including a top metal level that is disposed furthest from the surface of the plurality of levels; a bottom electrode, said bottom electrode positioned over the top metal level and conductively contacting a first conductor of said top metal level; a capacitor dielectric disposed over said bottom electrode; dielectric sidewall structures disposed adjacent to said bottom electrode; and at least a portion of said capacitor dielectric; and a top electrode, disposed over said capacitor dielectric and extending over at least one dielectric sidewall structure to conductively contact a second conductor of said top metal level.
 2. The integrated circuit of claim 1 wherein the capacitor dielectric is comprised of a high-k material.
 3. The integrated circuit of claim 2 wherein said capacitor is TaO_(x).
 4. The integrated circuit of claim 1 wherein said bottom electrode is comprised of a layer of TaN and a layer of TiN.
 5. The integrated circuit of claim 1 wherein said top electrode is comprised of a layer of TiN and a layer of TaN.
 6. The integrated circuit of claim 1 wherein said dielectric sidewall structure are comprised of SiN.
 7. The integrated circuit of claim 1 wherein said conductors in said top metal level are comprised of Cu.
 8. The integrated circuit of claim 1 wherein said first conductor is coupled to a power supply rail.
 9. The integrated circuit of claim 1 wherein said second conductor is coupled to ground.
 10. The integrated circuit of claim 1 wherein said top metal level capacitor is a decoupling capacitor from a supply voltage to ground.
 11. The integrated circuit of claim 1, wherein the top electrode comprises: a first layer disposed over and adjacent to the capacitor dielectric; and a conductive strap disposed over and in contact with the first layer, and extending over the at least one dielectric sidewall structure to the second conductor of the top metal level.
 12. The integrated circuit of claim 11, wherein the conductive strap comprises a diffusion barrier material.
 13. The integrated circuit of claim 11, wherein the dielectric sidewall structures are also disposed adjacent to at least a portion of the first layer of the top electrode.
 14. An integrated circuit including a top metal level capacitor comprising: a plurality of levels of metal conductors disposed near a surface of a semiconductor substrate, the plurality of levels including a top metal level comprised of copper that is disposed furthest from the surface of the plurality of levels; a bottom electrode comprised of a layer of TaN and a layer of TiN, said bottom electrode positioned over and in contact with a first conductor of said top metal level; a capacitor dielectric comprised of TaO_(x) and disposed over said bottom electrode; dielectric sidewall structures comprised of SiN and disposed adjacent to said bottom electrode, and at least a portion of said capacitor dielectric; and a top electrode comprising a first layer comprised of TiN disposed over and in contact with the capacitor dielectric, and a strap layer comprised of TiN that is disposed over first layer and that extends over at least one dielectric sidewall structure to conductively contact a second conductor of said top metal level. 